import cv2
import time


stream = cv2.VideoCapture('v4l2src ! video/x-bayer, format=bggr, width=640, height=480 ! bayer2rgb ! videoconvert ! appsink')
qr_detector = cv2.QRCodeDetector()


def read_qr():
    try:
        while stream.isOpened():
            _, frame = stream.read()
            frame = cv2.cvtColor(frame, cv2.COLOR_RGB2GRAY)
            if frame is None:
                print('unable to read from stream')
                break

            retval, points, straight_qrcode = qr_detector.detectAndDecode(frame)
            if retval:
                print('retval', retval)
                return retval
            else:
                print('.', end=' ', flush=True)
    except Exception as ex:
        print(ex)
        return None

while True:
    read_qr()


stream.release()